Conventionally, there has been an electric power conversion device, which is configured to bidirectionally convert DC power between a primary side and a secondary side thereof, to be used for charge and discharge of a storage battery, or the like. For example, in a state where the primary side is connected with a DC power supply and the secondary side is connected with the storage battery, the electric power conversion device is configured to convert DC power received from the DC power supply into desired DC power to be output to the secondary side, and accordingly, it is possible to allow the charge of the storage battery. On the other hand, in a state where the primary side is connected with a load and the secondary side is connected with the storage battery, the electric power conversion device is configured to convert DC power received from the storage battery into desired DC power to be output to the primary side, and accordingly, it is possible to allow the discharge of the storage battery.
As this type of electric power conversion device, there has been known a device (a bidirectional DC/DC converter), which has a function of mutually converting DC power between a first DC power supply or a first load, and a second load or a second DC power supply (see JP 2011-234541 A, hereinafter referred to as document 1). The electric power conversion device described in the document 1 includes: a primary side circuit including the first DC power supply or the first load; and a secondary side circuit including the second load or the second DC power supply; and a transformer that is between the primary side circuit and the secondary side circuit.
The electric power conversion device described in the document 1 further includes bridge circuits that are respectively disposed in the primary side circuit and the secondary side circuit, each of which is constituted by four semiconductor switches. The electric power conversion device is configured to, by synchronizing operations of semiconductor switches in the bridge circuits, supply electric power transformed with a transformation ratio of the transformer, from the primary side circuit to the secondary side circuit, or supply electric power transformed with the transformation ratio of the transformer, from the secondary side circuit to the primary side circuit.
However, the electric power conversion device, which is configured to bidirectionally convert DC power with the transformer, cannot boost the DC power bidirectionally, because a direction of boosting the DC power is fixedly set, depending on the transformation ratio (a turn ratio) of the transformer. That is, when the electric power conversion device is configured to boost DC power, as the electric power conversion, toward the secondary side from the primary side, DC power is stepped down in a case where the electric power conversion is performed in a reverse direction (toward the primary side from the secondary side). For this reason, when the electric power conversion device is used for charge and discharge of the storage battery for example, it is impossible to perform such use as boosting, upon charge of the storage battery, DC power received from the DC power supply to allow charge of the storage battery, and, upon discharge of the storage battery, boosting DC power received from the storage battery to be supplied to the load.